Quarks and gluons have never been observed freely in nature. Hence, there must be a reason, why they only appear in combination with other particles. The corresponding mechanism is called confinement.
Renormalizationgroup arguments yield a large effective coupling for large quark separation. ' This suggests that perturbation theory may break down at large distances, which would explain the lack of perturbative evidence for confinement. Eliminating ultraviolet divergences with the artifice of a lattice, Wilson has investigated the strong-coupling limit of gauge theories. ' In this limit the theory becomes one of quarks connected by strings, and confinement is natural.
Topological tunneling and Goldstone gluons by Michael Creutz and Thomas N. Tudron
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